Shenzhen plans to begin charging motorists congestion fees after the third phase of its subway network is completed in 2016.

The city announced last week that there were two million registered vehicles on its streets, the second highest in any mainland city, trailing only Beijing.

Xu Wei, deputy director of Shenzhen's traffic police bureau, was quoted by the Yangcheng Evening News as saying that the city ranked first on the mainland in terms of vehicle density, with 300 vehicles for every kilometre of road. Xu said a density figure of 270 was recognised as alarming in other countries.

The traffic police bureau announced on Sunday it would collect the congestion fee when the city's public transport network improved with the opening of phase three of the Shenzhen Metro, adding five new lines and more than 100 stations.

The city authorities also announced measures to reduce the use of vehicles in an attempt to relieve traffic congestion.

According to a 'green commuting' programme announced on Sunday, a number of incentives will be offered to vehicle owners who voluntarily reduce their car use. Those who take their cars off the roads for more than 30 days of their own choosing will be rewarded with stickers which will entitle them to discounted parking fees and insurance premiums.

The city will also restrict the use of government cars and vehicles that fail to meet national exhaust emission standards. Government cars will be out of action on one workday a week and civil servants will also be required to leave their cars at home on certain days.

The programme was first introduced as a temporary measure for the World University Games in Shenzhen in August. About 160,000 people volunteered not to drive during the games, although they did not receive any rewards.

People said they welcomed the programme, but doubted it was practical. One vehicle owner, Zhang Aiping, said she was not sure how the government would monitor whether a driver was using their car on any given day. She said it would also be complicated to demand the parking fee and insurance premium discounts given as rewards for not driving.

The plan to charge a congestion fee also met with a sceptical response in an online survey, in which more than 70 per cent of respondents opposed the idea.

People said traffic congestion was not caused by vehicle owners, but by poor urban planning. Some suggested stricter curbs on the use of government cars.

The city first began planning to introduce congestion fees in 2007, when the number of Shenzhen-registered vehicles reached one million. That number has doubled in the five years since.

The government also suggested collecting congestion fees during the university games, but did not end up implementing the plan.

1,500

The number of electric buses and taxis made by BYD that Shenzhen plans to add to its public transport fleet to reduce pollution